38KV low current fused switch

ABSTRACT

A low current high voltage switch having a bridging contact comprising vertical contact probes entering arc extinguishing and confining bushings to engage the main contacts; the bridging contacts are driven in either direction by an overcenter spring operation. The switch is coordinated with a series fuse. The switch is preferably multi-pole and is truck mounted for insertion in a compartment by a racking mechanism which is interlocked with the operating mechanism to prevent operation of the racking mechanism when the switch is closed.

United States Patent [191 May et al.

[4 1 July 8,1975

[ 38KV LOW CURRENT FUSED SWITCH [75] Inventors: William E. May, Feasterville; Philip C. Netzel, Milmont Park, both of Pa.

[73] Assignee: I-T-E Imperial Corporation, Spring House, Pa.

[22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,461

[56] References Cited UNITED STATES PATENTS 677,455 7/1901 Von Kando 200/16 E 1,067,735 7/1913 Hewlett 200/163 UX 1,872,298 8/1932 Kehoe et al..... 200/50 AA 1,992,109 2/1935 Whitehead 200/243 X 2,058,656 10/1936 Anderson 200/144 R 2,140,149 12/1938 Arutunoff 200/163 UX 2,540,814 2/1951 Eichelberger... ZOO/50 AA 2,548,220 4/1951 Kelle 317/103 X 2,673,260 3/1954 Lester et al. 200/50 AA 2,778,895 1/1957 Hebbel et a1 200/50 AA 3,280,282 10/1966 Rodeseike et al 200/50 AA X 3,469,043 9/1969 Wilson 200/50 AA 3,783,208 1/1974 Davies et a1. 200/50 AA 3,783,209 1/1974 Cleaveland et a1. 200/50 AA FOREIGN PATENTS OR APPLICATIONS 1,316,389 12/1963 France 200/164 R Primary Examiner-James R. Scott Attorney, Agent, or Firm-Ostrolenk, Faber, Gerb & Soffen [5 7] ABSTRACT A low current high voltage switch having a bridging contact comprising vertical contact probes entering arc extinguishing and confining bushings to engage the main contacts; the bridging contacts are driven in either direction by an overcenter spring operation. The switch is coordinated with a series fuse. The switch is preferably multi-pole and is truck mounted for insertion in a compartment by a racking mechanism which is interlocked with the operating mechanism to prevent operation of the racking mechanism when the switch is closed.

9 Claims, 21 Drawing Figures mr-imu ms 3.894 204 SHEET 3 v PATENTEPJUL 8 I915 SHEET MMQ NQ m

QN E PATENTEUJUL 8 I915 SHEET DATEWFPJUL 8 I915 3,894; 204 SHEET 8 SHEET :4 l n In A m: v rbn 6i l 2 cl: F: El: FL In. In

NEW-F JUL I975 -NMN I N SHEET QNE 38KV LOW CURRENT FUSED SWITCH The present invention relates to a low current high voltage switch for use in electrical systems of the order of up to 38 kilovolts. High voltage metal clad switchgear construction often requires that primary control power as well as power for heating and lighting be provided from the high voltage line through an auxiliary power transformer. This requires a high voltage low current switch that is complementary to the metal clad switchgear.

The present novel switch includes interrupting means which consists of two interrupter well bushings connected in series by a contact bridge assembly with two are followers and contact rods. This bridge assembly is actuated through an insulated push rod by an overcenter spring mechanism. The interrupter assembly is in turn connected in series with a high voltage current limiting fuse.

The switch is mounted on a rollout truck and is installed in a switchboard. Connection between the switchboard and the switch is achieved through a capacitively graded bushing of appropriate material.

In the present invention the overcenter spring mechanism is operated through a right angle drive and a telescoping actuating shaft. The telescoping shaft extends out from the switch as the switch is racked into the switchboard. This allows the switch to be operated with the front door of the switchboard compartment closed.

Load current interruption takes place within the well bushings. As the contact rods of the bridge assembly are drawn out of the well bushings, arcs are established within the bushings. An arc follower on the end of each contact rod aids in interruption.

The maximum let-through current of the current limiting fuse is coordinated with the momentary current rating of the well bushings. The well bushings are themselves mounted in an appropriate molding of insulating material such as epoxy which also serves as a guide for the moving contact bridge assembly and operating push rod. The epoxy molding straddles the main moldings and provides terminals for connection to the lower bushing and to the lower end of the current limiting fuse.

The primary object of the present invention is the provision of a high voltage low current switch having spring controlled snap action closing and opening oper- FIG. 1 is a schematic view of the novel switch of the present invention mounted on a truck and partly retion fully racked into the switchboard'but with the contacts open.

FIG. 3 is a view corresponding to that of FIG. 2 showing the contacts closed. v

FIG. 4 is a side view'of thenovel low current high voltage switch 'of the present invention. FIG. 4 corresponds to the schematic illustration shown in FIG. 2.

FIG. 5 is an enlarged view of a portion of the novel switch of the present invention showing the contacts closed.

FIG. 6 is an enlarged schematic view showing the operating mechanism for the switch in conjunction with the racking mechanism. I

FIG. 7 is a further enlarged side view of the operating mechanism shown at the bottom of FIG. 5 and i n FIG. 6; FIG. 7 is taken on line 77 of FIG. 8 lookihg in the direction of the arrows. i I I FIG. 8 is a top view of the operating mechanism of FIG. 6.

FIGS. 9, 10 and 11 are detailed views of the racking interlock mechanism. FIG. 10 is a view partly in crosssection taken from line l010 of FIG. 11..FIG. 11 is a view partly in cross-section taken from line 1,1"11 of FIG. 10.

FIG. 12 is a front view of the switch showing fuse mounting and operating elements.

FIG. 13 is a view of the lower fuse contact line ,I414 of FIG. 12.

FIG. 14 is a view of the upper fuse contact taken fromIine 1313 of FIG. 12.

FIG. 15 is a view corresponding to FIG. 12 showing the entire three pole switch.

FIG. 16 is a bottom plan view of the switch showing the racking and switch operating arrangement.

FIG. 17 is a detailed front view of theoperating and taken from racking elements of the switch.

FIGS. 18 and 20 are views of the operating elements of the switch and the connections to the main operating shaft. FIG. 20 is a view partly in cross-section taken from line 20-20 of FIG. 21.

FIGS. 19 and 21 are views of the racking mechanism interlock. FIG. 21 is a view partly in cross-section taken from the line 2l2l of FIG. 20.

Referring first to FIGS. 1, 2 and 3, the high voltage switch is mounted on a truck having appropriate wheels 31 which enable the entire switch unit to be rolled into the compartment 33 of a switchboard and to be locked therein. The truck 30 therefore carries all of the elements of the switch in a manner hereinafter described including the front panel 35 which may be' opened for servicing of the switch after the truck 30 has been moved out of the switchboard compartment 33. The compartment 33 has the recessed rear top wall 42 (FIGS. 1, 2 and 3 which is part of the low profile structure.

The truck 30 carries the upper back connection stud 40 which in turn is carried inan appropriate insulator 41 on the frame 330 of the switch and which terminates in appropriate back disconnect contacts 43. The truck also carries the lower back connection stud 45 in its insulator 46, the back connection having the back disconnect contacts 47.

The rear walls 50, 51 of the switchboard have appropriate openings 52, 53 through which the back connection studs 40 and 45 may enter to establish contact with appropriatebusses leading, in this case, to the primary winding of the auxiliary power transformer (not shown)."jwhen the switch is fully racked into the switchboard compartment 33 from the position of FIG. 1 to the positions of FIGS. 2 and 3. I g

The low profile structure is of the type shown in US. Pat. No. 3,735,065, assigned to the assignee of the present invention. I I

The interrupter switch is series connected from the back connection studs 45 through the stationary contactassembly 60 and through the bridging contact assembly 61 to the current limiting fuse 62 and then to the upper back connection stud 40. This enables the interrupting capacity provided in the stationary contact assembly 6010 be coordinated with the interrupting capacityof the current limiting fuse 62. A racking mechanism'Khereinafter described morecompletely in connection with FIGS. 6-16) is provided in order to move the truck 30 and the switch carried thereby to various positions within the housing. The racking mechanism serves as hereinafter described to interlock the switch gear on the truck 30 in the compartment so that the switchgear cannot be withdrawn from the compartment when the contacts are closed and provides also for various positions of the switchgear in the compartmenf'includingz a fully racked in position where the back connection studs 40 are connected appropriately to busses behind the compartment, a partially racked out position where the back connection studs are disconnected from their source of power but the moving bridging contact 61 may be operated for test purposes and an unlocked position where the switchgear may be completely racked out of the compartment provided the bridging contacts 61 are in the open circuit position. The operating rod 100 for the bridging Contact 61 is more specifically described in connection with FIGS. 4 to 7 but essentially consists of a spring driven closing member; an operator is provided to drive the spring from one overcenter position in which the contacts 61 are in one condition (open or closed) to another overcenter condition in which the contacts 61 are in the other position (closed or open). As seen in FIGS. 1 to 5 the stationary contact structure 60 comprises an insulating structure 70 supported between the conductors 71 and 72, conductor 71 being secured to the lower contact structure 83 for the fuse 62. Conductor 71 is secured at its opposite end to the lower back connection stud 45.

The upper end of the fuse 62 is connected to the upper contact structure 73 (FIG. 4) for the fuse which in turn is connected to the upper back connectionstud 41. It will thus be seen that in the event the fuseis utilized to interrupt the current, the fuse 62 may readily be removed from the contacts 73 and 83 and another fuse replaced. The fuse contacts are also seen in FIGS. 13 and 14 in detail and in FIG. 12. This type of contact structure for a fuse is well known and requires no further description herein. Also the concept of coordinating a fuse with an interrupter is well known and requires no further description at this point.

The operating mechanism for the switch is essentially similar to that shown in application Ser. No. 396757 filed Sept. 13, 1973 now US. Pat. No. 3830994 and assigned to the assignee of the present invention. It may also be of the type shown in application SenNo.

406,473 filed Oct. 15, 1973, assigned tothe assignee of The preferred method of operating operating rod of the bridging contact 61 is through an overcenter spring arrangement which in effect will provide a charged spring for operation in either direction and thereby insure a smooth continuous and rapid operation so that any arc which may be drawn will not hang in an intermediate position of the contacts but will be rapidly extinguished by the continuity of movement from the position of FIG. 1 to the position of FIG. 2.

The operating means for the rod 100 comprises a bell crank 114 which is loosely mounted on the shaft 115. Pin 113 of bell crank 114 is connected to the link 103 which in turn is connected by pin 104 to link 105. The opposite end of link 105 is connected by pin 106 to an extension 107 of the rod 100. Thus as the bell crank 114 is rotated about the shaft 115 the direction of rotation of the bell crank 114 will either act to push the bridge contacts from the solid line position of FIG. 5 to the dotted line position or in the opposite direction to pull the push rod 100 up back to the solid line position. The pin 116 is connected to toggle link 117 which through the toggle pin 118 is connected to toggle link 119, the opposite end of which is connected and rotatably mounted on the pin 120. A tension spring 131 is connected between the pin 132 at the outer end 133 of the spring carrying member and the toggle pin 118 of the toggle 116-119. When the-spring carryinglink 130 is moved from the position shown in FIGS. 3 and 5 to the position shown in FIGS. 1 and 2 and through the various positions shown in FIG. 7 the spring 131 serves as it passes from one side of the toggle link 119 to the other side of the toggle link 119 to draw the toggle 117-119 toward a collapsed position inthe direction of tension of the spring.

The collapse of the toggle from the position shown in FIG. 3 thereby pulls on the pin 116 driving the bell crank lever 114 counterclockwise and driving the push rod 100 carrying the bridge assembly 61 in the opening direction. When the spring carrying link 130 is moved from the position of FIGS. 1 and 2 back to the position of FIGS. 3, 4 and 5 then as the spring 131 passes through the point of alignment with the toggle link 119 to the underside of the toggle it draws the toggle 117-119 from the positionof FIGS. 1 and 2 back to the position of FIGS. 3 and 5 thereby resulting in closing of the switch. I I

The means for moving the tension spring carrier 130 from the position of FIGS. 1 and 2 to the position of FIGS. 3,4 and 5 and back again includes the crank which has the extensions 141 and 142. The spring carrier 130 is provided with a bearing pin 144 which is engageable by either of the extensions 141 or 142 on the crank 140. I

Crank 140 is keyed to the shaft 115. When the shaft 115 is rotated in one direction then the extension 142 will raise the pin 144 to operate the spring carrier 130 so that the spring 131 moves to the opposite side of the toggle center and collapses the toggle toward an opening direction for the switch.

On a reverse movement of the shaft 115 the extension 141 now engages the pin 144 and results in a clos- FIG. 8 shows the actual construction of the link arrangement in which the tension springs 131 actually comprise a pair of tension springs 131. and 131b on the 2 pins 132 in the carrier 130, the carrier having the operating pins 144 and the carrier 130 also being freely rotatable mounted on the shaft 115. The toggle 117-119 may also readily be seen as well as the bell crank lever 114 which also is loosely mounted on the shaft 115. The operating crank 140 and its upper extension 141 mayreadily be seenincluding its cooperation with the pin 132 as well as the link connection through link 105 to extension 107 and pin 106 of the contact operating shaft. 1

The contact structures may be understood more readily from FIGS. 5 and 12 in which the bridging contact 61 comprises an insulating carrier 200 mounted on the operating shaft 100 and provided with vertically aligned bridging contact members 201, 202 which have appropriate contact tips 203, 204 of material which will resist an arcing condition.

In essence then the bridging contact elements 201, 202 are probe members connected electrically to a conductive cross strap 210 by which they are bridged together.

The stationary contact support 60, as previously pointed out, is basically of an epoxy material as is the bridging member support 61. Appropriate stationary contacts 220, 221 are located in the recesses 223, 224 of the insulating support 60 for the stationary contact. These stationary contacts 220, 221 are engaged by the ends of the contact probes 201, 202 of the bridging contact structure 61 when the structure is moved to the solid line closed circuit position of FIG. 5 and are disengaged when the structure is moved to the dotted line position of FIG. 5 or the position shown schematically in FIGS. 1 and 2. Y

The housing 60 for the stationary contact structure in addition to the recesses 223, 224 is provided with bushings 230, 231 which serve to encase the moving contact elements 201', 202 when they are fully inserted in bridging relation with the contacts 220 and 221. These bushings are also of an epoxy or other insulating material similar to that utilized for the housing 60 of the bridging contacts and serve as an arc extinguishing chute for'attenuating, confining and "extinguishing the are as the arc is drawn down the tube when the moving contacts 201,202 are moved from the solid line to the dotted line' position of FIG. 5 or from the position of FIG. 3 to the position of FIGS. 1 and 2.

The conductor strap 71 leading to the lower contact structure 73 of the fuse 62 is connected to the conductor 250 which in turn is connected to stationary contact 221. Similarly the conductor strap 72 for the upper back connection stud 40 is connected to the conductor 251 which in turn is connected to the stationary contact 220.

By this means therefore a simplified method is provided for operating a low current switch from a closed to an open position and extinguishing the low current arc. 1

It should also be noted that the profile of the switch is arranged to accommodate itself to the relatively low volume smallsize high voltage switchboard of the type already described in U.S. Pat. No. 3,735,065 assigned to the assignee of the present invention.

ating shaft 310 in the truck (See also FIGS. 16 and 17). The rotation of the shaft 310 by a handle which may be connected and disconnected from the free end 311 thereof will, through the worm gear arrangement 300 shown in detail in FIGS. 18 and 20, operate the switch shaft 115 to move the switch between the open and closed positions of FIGS. 2 and 3. The switch is also provided with a jack shaft 320 which will operate. the three pole arrangement of the type shown in FIGS. 12 and 13. The jack shaft 320 is provided with a crank 321 which is connected to the pin 104 of the operating mechanism of FIG. 5 and the crank 321 and the jack shaft 320 are accordingly operated downwardly or clockwise when the switch is open and upwardly. or counterclockwise when the switch is closed. Jack shaft 320 is provided with similar cranks 321a and 321b keyed to the jack shaft 320 at each of the three pole switch locations so that as seen in FIGS. 12 and 17 the operating mechanism for the center of the three pole switch may be utilized to operate the whole .set of switches.

Also in FIGS. 12, 13 and 14 the fuse arrangement is shown whereby the fuse 62 is engaged by the upper contact arrangement 73 and by the lower contact arrangement 83 and the structure 330 which supports the fuse contacts is shown for one of the poles of the three poled switch but is obviously usable for each of the other poles as well so that each of the switches may be coordinated with its individual fuse.

The switch operating shaft 310 is a telescoping shaft which may slide into the shaft 310a, being appropriately shaped to operate the same so that the switch operating shaft will be available for actuation of the truck FIGS.. 9, 10, 11 carries a bracket 361 on which is mounted the small shaft 362. Bell crank lever 363 is pivotally mounted on the shaft. One end of the bell crank lever carries indicia tabs 364 to show the closed or open position of the switch. These tabs are visible through a window 365 (FIG. 9) in the front side frame 360 of the switch. The opposite end of bell crank lever 363 is connected by pin 365a to the drive lever 366 which in turn'is connected by the pin 367 to the link 368 connected by pin 369 to a crank 370 on the jack shaft 320. The rotation of the jack shaft 320 will thereby operate the bell crank lever 363 to present the closed or open indicia to view through the window thereby signalling the condition of the switch.

The racking mechanism for inserting the truck into the compartment and for moving thetruck in the compartment is shown in FIGS. 6 and 16. Crank arms 500a and 500b carry rollers which engage in fixed cam plates in the compartment. The racking shaft 400 has an external thread which engages with a nut 501 fixed to a bracket at the front of the truck. Clockwise rotation of the shaft 400 will cause the shaft to advance out of the front of the truck. A clevis 402 is slidably mounted on the shaft 400. This clevis 402 is positioned between two collars 401 which are pinned to the shaft 400 and rotate with it. As the shaft is moved by its reaction with the nut 501, the clevis 402 is moved-with it. Links 502 are connected between fixed pins extending outward from the sides of the clevis 402 to a crank on the cross shaft 503. Movement of the clevis 402 along shaft 400 causes shaft 503 to be rotated by the action of the aforementioned links 502 and the cross shaft crank. Crank arms 500a and 5001) are fixed to the ends of cross shaft 503 and are also rotated by the action of the 502 links and crank. As the crank arms 500a and 500b are rotated, they engage with a slotted cam surface in the fixed cam plates in the compartment. Clockwise rotation of the racking shaft 400 causes the breaker to advance into the compartment and counter clockwise ro tationof shaft 400 will cause the breaker to move out of the compartment. The shaft 400 is provided with two blind holes which are engaged by stop link 403 fixed to the square interlock shaft 80 to provide for stopping the racking mechanism in the connect and disconnect positions in the compartment.

When the breaker reaches one of the stopped positions, the'stop link 403 on the square interlock shaft 80 automatically engages with the hole in the racking shaft 400and prevents further rotation of the racking shaft. The racking mechanism can only be released from a stopped position by rotation of the interlock shaft 80 by the lever 81 at the front of the breaker.

The racking mechanism and the switch operating mechanism are interlocked so that l. the switch cannot be moved from a stopped position (connect or disconnect) unless the switch contacts are open.

2. the switch cannot be closed unless the racking mechanism is in a stopped position.

3. the racking mechanism can be padlocked in either the connect or disconnect position. This padlocking prevents moving of the switch from the stopped position but does not interfere with the operation of the switch mechanism.

Interlocking between the racking mechanism and the switch operating mechanism is accomplished in the following manner.

If the racking mechanism has been operated to move the switch truck to one of the stopped positions, the switch operating mechanism can then be operated to close the switch contacts. On the closing of the switch contacts, the jack shaft 320 is rotated in a counter clockwise direction. This causes link 368 to drive the interference link 512 in a clockwise sense. An extension on link 512 is thus positioned above the end oflink 510 prohibiting the rotation of link 510. The racking mechanism interlock shaft 80 is thus prevented from rotating and the racking shaft 400 cannot be rotated since it is held by the stop link 403.

When the switch operating mechanism is operated to open the switch contacts, the jack shaft 320 is rotated clockwise and through link 368 rotates interference link 512 counter clockwise and permits rotation of the square interlock shaft 80 by handle 81. This action retracts the stop link 403 from the hole in the racking shaft 400 and permits movement of the switch truck by the racking mechanism.

Rotation of the indexing shaft 80 by the handle lever 81 in a clockwise direction sets up the interlock to prevent operation of the switch mechanism when the switch truck is in an intermediate position between the fixed stopped positions. When the square indexing shaft 80 is rotated clockwise, spring 424 applies tension 510 cannot return to its counter clockwise position until a stopped position of the racking mechanism is reached. Shaft is prevented from rotating counter clockwise by the action of the stop link 403 on the surface of shaft 400 between the indexing holes.

Padlocking of the racking mechanism can be accom-- plished when the switch truck is in one of the indexed positions in the compartment. Link 513 is moved toward the front of the switch. This causes an interference with the lever 510 and prevents racking of the switch by preventing release of the stop link 403 from the indexing hole in shaft 400. When the link 513 is drawn forward a slotted hole is exposed. A padlock can then be inserted.

In the foregoing, the present invention has been described in connection with preferred illustrative embodiments; it is therefore preferred that the scope of the invention be determined, not by the specific disclosures herein contained, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A low current switch comprising a movable bridging contact structure having an insulating transverse support and a pair of parallel contact probes extending therefrom;

said support having a conductor electrically interconnecting said probes;

a stationary contact structure having an insulating support extending substantially normal to said contact probes;

a pair of stationary contacts carried by said stationary contact structure;

means for connecting each of said stationary contacts in circuit;

said movable bridging contact structure and its contact probes being movable in a direction longitudinally of said probes toward and away from said stationary contacts, each of said probes being engageable with one of said stationary contacts on such longitudinal movement toward said stationary contacts;

said insulating support for said stationary contacts having a pair of insulating bushings,

each bushing extending from a stationary contact toward said movable contact structure;

each of said bushings being aligned with one of said probes;

means for moving said bridging contact structure toward and away from said stationary contact structure,

said movable contact probes entering said bushings and engaging said stationary contacts, when the movable contact structure is moved toward said stationary contact structure,

said bushings acting as are confining structures when said contacts are open.

2. The low current switch of claim 1 in which an overcenter spring operating mechanism is provided comprising a main operating toggle;

said operating toggle having a pair of links and a pin connecting said links; the first of said toggle links being pivotally stationarily mounted at the end opposite said pin; and operating shaft; a connecting drive between said toggle and said operating shaft; the second of said toggle links being pivotally connected at the end opposite the pin to said connecting drive; a second driving connection between said operating shaft and said movable contact structure;

a tension spring and an operating handle;

said operating handle being rotatably mounted on a stationary pivot for operation in a plane parallel to said toggle; said tension spring being connected between said pin of said toggle and a portion of the operating handle remote from the pivotal mounting of said handle;

said spring snapping the handle, toggle, operating shaft and moving contacts from closed to open and open to closed positions on movement of the handle to cause the tension spring to pass the said pin of the toggle.

3. The low current switch of claim 2 wherein said switch comprises a plurality of similar contact assemblies; said contact assemblies being arranged parallel to each other;

a housing for said plurality of control assemblies; said housing including supports for said contact assemblies;

a jack shaft supported in said housing and running transversely to said contact assemblies;

.one of said contact assemblies having said operating shaft, operating toggle and the aforesaid drive connection, spring and handle;

said jack shaft being connected to and rotatable by the said operating shaft of said one contact assembly and being interconnected to each of the other .contact assemblies for simultaneous operation.

4. The low current switch of claim 3 wherein the circuit connected to one of said stationary contacts in each contact assembly includes a pair of spaced fuse contacts; and a coordinated fuse mounted between said fuse contacts.

5. The low current switch of claim 3 in which said switch is mounted on a truck;

a telescoping operating shaft extending along said truck;

a connection between said telescoping operating shaft and said first mentioned operating shaft.

6. The low current switch of claim 5 a compartment said truck being movable in said compartment;

the said telescoping operating shaft being extensible and collapsible in the direction of movement of the truck in said compartment,

the end of said telescoping operating shaft being accessible at all positions of said truck in said compartment.

7. The low current switch of claim 6 said compartment having an upper back disconnect contact and a lower back disconnect contact for each pole;

each pole having complementary back connection studs; one of said studs being connected to the said fuse contact; and the other of said studs being connected to the other of said stationary contacts.

8. The low current switch of claim 7,

said truck having a racking shaft extending parallel to said telescoping operating shaft;

and an interlock between the racking shaft and the switch operating shaft; said racking shaft being locked against operation in the closed circuit position of the switch.

9. The low current switch of claim 7 in which the upper back connection stud and the lower back connection stud terminate in horizontally spaced vertical planes; and the disconnect contacts of the compartment are similarly spaced. 

1. A low current switch comprising a movable bridging contact structure having an insulating transverse support and a pair of parallel contact probes extending therefrom; said support having a conductor electrically interconnecting said probes; a stationary contact structure having an insulating support extending substantially normal to said contact probes; a pair of stationary contacts carried by said stationary contact structure; means for connecting each of said stationary contacts in circuit; said movable bridging contact structure and its contact probes being movable in a direction longitudinally of said probes toward and away from said stationary contacts, each of said probes being engageable with one of said stationary contacts on such longitudinal movement toward said stationary contacts; said insulating support for said stationary contacts having a pair of insulating bushings, each bushing extending from a stationary contact toward said movable contact structure; each of said bushings being aligned with one of said probes; means for moving said bridging contact structure toward and away from said stationary contact structure, said movable contact probes entering said bushings and engaging said stationary contacts, when the movable contact structure is moved toward said stationary contact structure, said bushings acting as arc confining sTructures when said contacts are open.
 2. The low current switch of claim 1 in which an overcenter spring operating mechanism is provided comprising a main operating toggle; said operating toggle having a pair of links and a pin connecting said links; the first of said toggle links being pivotally stationarily mounted at the end opposite said pin; and operating shaft; a connecting drive between said toggle and said operating shaft; the second of said toggle links being pivotally connected at the end opposite the pin to said connecting drive; a second driving connection between said operating shaft and said movable contact structure; a tension spring and an operating handle; said operating handle being rotatably mounted on a stationary pivot for operation in a plane parallel to said toggle; said tension spring being connected between said pin of said toggle and a portion of the operating handle remote from the pivotal mounting of said handle; said spring snapping the handle, toggle, operating shaft and moving contacts from closed to open and open to closed positions on movement of the handle to cause the tension spring to pass the said pin of the toggle.
 3. The low current switch of claim 2 wherein said switch comprises a plurality of similar contact assemblies; said contact assemblies being arranged parallel to each other; a housing for said plurality of control assemblies; said housing including supports for said contact assemblies; a jack shaft supported in said housing and running transversely to said contact assemblies; one of said contact assemblies having said operating shaft, operating toggle and the aforesaid drive connection, spring and handle; said jack shaft being connected to and rotatable by the said operating shaft of said one contact assembly and being interconnected to each of the other contact assemblies for simultaneous operation.
 4. The low current switch of claim 3 wherein the circuit connected to one of said stationary contacts in each contact assembly includes a pair of spaced fuse contacts; and a coordinated fuse mounted between said fuse contacts.
 5. The low current switch of claim 3 in which said switch is mounted on a truck; a telescoping operating shaft extending along said truck; a connection between said telescoping operating shaft and said first mentioned operating shaft.
 6. The low current switch of claim 5 a compartment said truck being movable in said compartment; the said telescoping operating shaft being extensible and collapsible in the direction of movement of the truck in said compartment, the end of said telescoping operating shaft being accessible at all positions of said truck in said compartment.
 7. The low current switch of claim 6 said compartment having an upper back disconnect contact and a lower back disconnect contact for each pole; each pole having complementary back connection studs; one of said studs being connected to the said fuse contact; and the other of said studs being connected to the other of said stationary contacts.
 8. The low current switch of claim 7, said truck having a racking shaft extending parallel to said telescoping operating shaft; and an interlock between the racking shaft and the switch operating shaft; said racking shaft being locked against operation in the closed circuit position of the switch.
 9. The low current switch of claim 7 in which the upper back connection stud and the lower back connection stud terminate in horizontally spaced vertical planes; and the disconnect contacts of the compartment are similarly spaced. 